With a general image capturing device, the projection method expressing the relationship of a half view angle θ and an image height y adopts an imaging optical system having a perspective projection expressed substantially as y(θ)=f*tan θ by using a paraxial focal length f of the imaging optical system. Distortion is sometimes corrected as needed. With the foregoing perspective projection method, change in the image height per unit view angle tends to increase considerably at the wide angle side that is separated from the optical axis of the imaging optical system. Accordingly, in order to widen the image capture range, a large imaging element (image sensor) is required to capture the image height y. For instance, if the maximum view angle of image capture is 90°, since the image height y will diverge, an infinitely large imaging element will be required, and an imaging optical system cannot be realized. Thus, as a projection method of capturing images at a wide angle with a finitely large imaging element, orthogonal projection y(θ)=f*sin θ is known. With the foregoing orthogonal projection method, even if the half view angle θ is 90°, since the image height y is finite, an image can be formed on the imaging element. According to the foregoing projection method, an image can be formed on the imaging element up to the half view angle being 90°. As a projection method for capturing images at a wider view angle than the foregoing orthogonal projection, there is an optical system having projection characteristics expressed with the expression y=a*f*sin(b*θ). Here, 0<a<sin θmax, b=π/(2*θmax), f: paraxial focal length of entire system, θ: half view angle (diagonal view angle of radian unit), θmax: maximum half view angle (diagonal view angle of radian unit), and y: actual image height on the light-receiving surface of the imaging element (refer to PTL 1).